Add explicit support for being installed into a system triggered with --enable-fhs...

Add explicit support for being installed into a system triggered with --enable-fhs-paths.

Add two mechanism for avoiding name-collisions in a system-wide
installation of charybdis. The ssld and bandb daemons, intended to be
directly used by ircd and not the user, install into libexec when
--enable-fhs-paths is set. For binaries which are meant to be in PATH
(bindir), such as ircd and viconf, there is now an option
--with-program-prefix=progprefix inspired by automake. If the user
specifies --with-program-prefix=charybdis, the ircd binary is named
charybdisircd when installed.

Add support for saving the pidfile to a rundir and storing the ban
database in localstatedir instead of in sysconfdir. This is, again,
conditional on --enable-fhs-paths.

Fix(?) genssl.sh to always write created SSL key/certificate/dh
parameters to the sysconfdir specified during ./configure. The
previous behavior was to assume that the user ran genssl.sh after
ensuring that his current working directory was either sysconfdir or a
sibling directory of sysconfdir.